The volcanic Kermadec Island peaks are a remote outpost that are generally uninhabited aside from a weather station and a hostel for visiting New Zealand scientists.
The 7:03 a.m. Thursday (1903 GMT Wednesday) quake was 29.8 miles (48 kilometers) deep, the USGS said.
The Pacific Tsunami Warning Center, a U.S. agency, issued a warning for possible tsunami damage in the Keramecs, Tonga and New Zealand. It said a tsunami measured at 2.2 feet (0.68 meters) was measured at Raoul Island in the Kermadecs.
The Kermadecs are about 570 miles (920 kilometers) south of Tonga, the nearest major island, and are 736 miles (1185 kilometers) northeast of Auckland, New Zealand.